public static string GetGuarReturnCode() { GuarReturnDT guarReturnDT = new GuarReturnDT(); string mmyy = getMMyy(); DataTable invoiceTable = guarReturnDT.GetByCond("Code like 'TK" + mmyy + "%'", " Code DESC"); string prefix = "TK" + mmyy; string suffix = "0001"; if (invoiceTable != null && invoiceTable.Rows.Count > 0) { suffix = getSuffix(invoiceTable.Rows[0]["Code"].ToString()); } return(prefix + suffix); }